Yeah it's definitely a difficult decision to make. On the one hand, no one deserves to be subjected to the torture of living in a cult, least of all children that are raised in it. On the other hand, I know personally of the heartache and abuse that you have to be prepared to subject yourself to in order to try and wake someone up from this cult. Some are able to wake up their wives, others (like me) fail miserably. I've read many accounts and tried to help some who were in a similar situation to yours, and it often ends badly. I'm sure the failures are disproportionately represented in the posts here due to the fact that in the case of success people don't have as much to talk about, but even so the cost can be very high.
Take solace in the fact that, according to a Pew survey on religion, fully 2/3rds of born-in JWs eventually leave the cult. Her children, being raised by a single mother from the sound of it, stand an especially good chance of making it out because she will be unable to put the same level of pressure on them as a pair of JW parents can do. They've also seen first hand that JW life isn't all perfect families and happy marriages as the JWs like to claim.
You've done her a great kindness already, and I suspect that even if you move on you'll be willing to provide her with the start of a support system out of the cult if she ever does decide to leave. That's a huge huge thing that you've already done. In my book you can move on not only with a clean conscience but knowing that you've done more than most would, and you've respected yourself in the process.